The present invention relates generally to a zoom lens and an imaging system incorporating the same, and more particularly to a high-zoom-ratio zoom lens well adaptable to electronic imaging devices such as CCDs or C-MOSs and an imaging system incorporating the same.
For zoom lens systems having high zoom ratios, comprising fewer lenses and having a short overall length, for instance, Patent Publication 1 has come up with a zoom lens comprising, in order from its object side, a positive first lens group, a negative second lens group, a positive third lens group and a fourth lens group, wherein all the lens groups move for zooming.
Zoom lenses having a zoom ratio of the order of 10 are disclosed in Patent Publications 2 and 3.
The zoom lens of Patent Publication 1 or the like has a zoom ratio of about 5; if the zoom ratio is brought up to about 10, its image-formation capability will become worse. A zoom lens having a zoom ratio of about 10 and primarily adapted to video cameras is set forth in Patent Publication 2 or the like.
Patent Publication 3 or the like has come up with a zoom lens that has a zoom ratio of about 10 and is designed to be received at a collapsible lens mount during storage, thereby achieving size reductions.
Patent Publication 1
JP(A)2004-12639
Patent Publication 2
JP(A)2005-242014
Patent Publication 3
JP(A)2006-133631
The zoom lens of Patent Publication 1 has a zoom ratio of about 5; if the zoom ratio is brought up to about 10, its image-formation capability will become worse, and its full length will grow long as well.
The zoom lens of Patent Publication 2 is of the type that is primarily used with video cameras or the like, and so it is unfit for slimming down a camera upon received at a lens mount, because of being based on the camera layout with the first lens group fixed relative to an imaging device.
The zoom lens of Patent Publication 3 has a zoom ratio of about 10, and is designed to be received at a lens mount upon storage, thereby achieving size reductions. However, its full length is long. Further, when multiple lens barrels received at the lens mount are extended out of it, it is still impossible to make the zoom lens received at the lens mount sufficiently thin, because of the requirement that the respective lens groups must be moved for zooming in the length of the extended lens barrels.